The present invention relates to a seismic generator. More particularly, the present invention relates to a seismic generator capable of generating seismic signals which can be detected at great distances either on the surface or underground.
Previous apparatus for communicating with persons underground has involved primarily electromagnetic energy-producing equipment. Such apparatus as has been used with a seismic energy-producing source has usually been restricted to an impulse source, such as the blow of a hammer. These prior art impulse sources characteristically produce a broad-band spectrum of energy with frequencies predominantly above about 100 cycles per second. Such higher frequency signals have a greater attenuation in rock than signals having frequencies below about 100 cycles per second. An additional drawback of the use of a hammer blow as the energy source is the danger of creating an underground explosion in areas where explosives may be present.
The present invention is directed to a seismic energy generator which can be operated either above or below ground and which requires only a small but steady input of energy to produce a signal of a frequency below about 100 cycles per second which can be easily detected and the position of the signal source determined at great distances either from the surface or underground. The present invention is adapted to permit a person trapped underground, for example, to transmit a seismic signal to facilitate the rapid location and recovery of the person trapped even in the absence of any means of power other than the manual power of the person himself. Location of the signal source can be by conventional methods including geometrical methods analogous to Loran or other routine navigational techniques. Reception of such a seismic signal provides an immediate indication that someone is alive underground, that rescue is desired and that someone is at the transmitter. Such an indication can be invaluable, for example, in the case of an underground disaster. Sharp impact between metal surfaces is not required in the apparatus of the present invention, with the result that the danger of creating an underground explosion as a result of operating the present apparatus is minimized.
The apparatus of the present invention includes a seismic generator which produces harmonic oscillations generated by rotating one or more eccentrically weighted masses. In one embodiment of the invention, weights may be attached to a plurality of flywheels and so positioned that, as the flywheels rotate, the weights are in phase when the weights are located in one predetermined plane but are out of phase when the weights are located in another plane which is perpendicular to the first predetermined plane. When more than one flywheel is employed, at least one flywheel should rotate in a direction opposite to that of the others. Rotation of the flywheels can be effected by the turning of a drive chain on a cycle apparatus which is powered either manually or by electric motor or other drive means.